Assembly of a flexible pipe and an end-fitting

ABSTRACT

An assembly of an end-fitting ( 9 ), having an axial extending through opening ( 14 ), with a flexible pressure pipe ( 1 ) which is of a non-bonded structure comprising a number of layers ( 2, 3, 4, 5, 7 ) including an inner carcass ( 2 ) of an interlocking structure made from metallic strips ( 23 ) forming a screwthread, an end part of which extends, in the assembled condition, into the through opening ( 14 ). The assembly comprises an annular holding groove ( 28 ) which is formed in the wall of the through opening ( 14 ), and a lock nut ( 15 ). The metallic strips ( 23 ) form a thread ( 24 ) with windings ( 25 ). When the pipe ( 1 ) is to be assembled with the end-fitting ( 9 ) the carcass ( 2 ) is exposed by initially removing the layers ( 3, 4, 5, 7 ) surrounding the carcass ( 2 ) at the end of the pipe ( 1 ), whereafter the lock nut ( 15 ) is screwed on to the end of the carcass. Finally the carcass ( 2 ) is inserted into the through opening ( 14 ) with the lock nut ( 15 ) placed in the holding groove ( 28 ) formed in the wall of the through opening ( 14 ). In some applications the lock nut ( 15 ) can also be embedded in a casting material (not shown), e.g. epoxy, for fixing the lock nut firmly in the holding groove. The joint between the carcass ( 2 ) of the flexible pressure pipe ( 1 ) and the end-fitting ( 9 ) is a simple and cheap structure and provides a greater resistance to axial tensile loads acting on the carcass ( 2 ) and against unwinding than has been known before.

BACKGROUND ART

The invention concerns an assembly of an end-fitting, having an axiallyextending through opening, with a flexible pressure pipe which is of anon-bonded structure comprising a number of layers including an innercarcass of an interlocking structure made from metallic strips forming ascrew thread, the end part of which extends, in the assembled condition,into the through opening.

Flexible pressure pipes are used in a variety of applications, includingwater supply lines, sewage lines and lines for transporting chemicalssuch as liquid ammonia and phosphoric acid and also high pressureoffshore flexible pipes for the oil and gas industry.

The joint between the carcass and the end-fitting must be able to resistthe axial tensile load acting on the carcass, when the flexible pipe isdescending over a great length. As the carcass is of an interlockingstructure of a type which allows a mutual screwing movement of thewindings of the metallic strips, the joint moreover must prevent thecarcass from becoming unwound.

Conventionally, such a joint is provided by screw shaped ribs which,during the extrusion of an inner lining of a plastic material around thecarcass, are pressed into the grooves between the windings such that thecarcass is secured by the lining which again is secured by theend-fitting. Owing to the notch sensitivity of the lining caused by thisconstruction, the lining is, however, inclined to crack.

This tendency is especially dangerous because temperature stresses canarise in the joint between the lining and the carcass, because theplastic material of the lining has a much higher coefficient ofexpansion than the material of the carcass, which could be of e.g.stainless steel.

SUMMARY OF THE INVENTION

The object of the invention is to provide an assembly of the typementioned in the opening paragraph in which the joint between thecarcass and the end-fitting is a simple and cheap structure and providesa greater resistance to axial tensile loads acting on the carcass andagainst unwinding of the carcass than has been known before.

This is achieved in that the assembly comprises an annular holdinggroove which is formed in the wall of the through opening, and a locknut which is screwed on the screwthread-formed strips of the end part ofthe carcass and fitted into the holding groove. In this construction thejoint between the carcass and the end-fitting is independent of theinner lining which moreover can be made with optimal strength. Whenfixed in the holding groove, the lock nut also prevents the carcass frombecoming unwound.

By interposing a galvanic insulation material having a high electricalresistance between the lock nut and the end-fitting, an electricpotential, which could cause galvanic corrosion, can be prevented fromarising between said parts.

The galvanic insulation material may advantageously be PTFE, preferablycontaining some solid insulation material for improving the pressurestrength and the form stability of the material.

In a simple and cheap embodiment, the galvanic insulation material canbe in the form of an annular disc placed on each side of the lock nut.In a particularly expedient embodiment, the lock nut can also be coatedwith the galvanic insulation material or totally manufactured from it.

The lock nut itself can be locked to the carcass by e.g. welding which,however, is time consuming and strenuous work and involves the risk thatsome of the plastic material of the pipe may be harmed by the heatgenerated by the welding process.

The lock nut can, however, in a very simple way be locked to the carcassby screwing a screw radially into the lock nut and against the carcass.This screw can advantageously be used to rotate the lock nut and therebytighten the carcass when the windings of this have been to some extentunwound.

For fixing the lock nut firmly in the holding groove of the end-fitting,the lock nut can be embedded in a casting material, e.g. epoxy.

The invention also concerns a method for assembling an end-fitting,having an axially extending through opening, with a flexible pressurepipe which is of a non-bonded structure comprising of a number of layersincluding an inner carcass of an interlocking structure made frommetallic strips forming a screw thread, an end part of which extends, inassembled condition, into the through opening. The method comprisesremoving the layers surrounding the carcass at the end of the pipe,screwing a lock nut on the screwthread-form strips of the end part ofthe carcass, and placing the lock nut in a holding groove formed in thewall of the through opening. This method can be performed in a quick andtime efficient manner in situ.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained more fully by the following description,given by way of example, with reference to the drawings, in which:

FIG. 1 shows, partly in axial section, a typical flexible pressure pipe,

FIG. 2 shows, in axial section, an assembly of the flexible pressurepipe shown in FIG. 1 and an end-fitting, and

FIG. 3 is a perspective view on an enlarged scale of a fragment of alock nut mounted on an carcass of the flexible pipe shown in FIG. 1.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 shows a flexible pressure pipe, which is generally designated by1. The pipe is of a non-bonded structure comprising a number of layerswhich in this embodiment are:

a carcass 2 of an interlocking structure made from metallic strips. Thecarcass serves, in the main, to prevent collapse of the pipe due to pipedecompression, external pressure, tensile armour pressure and mechanicalcrushing loads,

an inner lining 3 in the form of an extruded polymer layer for providinginternal fluid integrity,

a pressure armour 4 in the form of structural layers consisting ofhelically wound C-shaped metallic strips with a high lay angle,

a tensile armour 5 consisting of a pair of helically counter wound flatmetallic tensile wires 6 with a lay angle typically between 20° and 60°.The tensile armour serves to provide resistance to axial tensile loads,and

an outer sheath 7 in the form of an extruded polymer for shielding thestructural elements of the pipe from the outer environment and providingmechanical protection.

FIG. 2 shows an assembly 8 of an end-fitting 9 and the flexible pressurepipe 1. The end-fitting 9 forms the transition between the pipe and theconnector and for this purpose has a first part 10 with a connectionflange 11, a second part 12 and a third part 29. The three parts 10; 12;29 delimit a cavity 13 which partly is substantially cone-shaped. Theend-fitting 9 has furthermore a through opening 14 for accommodating anend of the pipe 1.

When assembling the flexible pressure pipe 1 with the end-fitting 9 theflat metallic wires 6 of the tensile armour 5 are led into the cavity 13in the end-fitting and a casting material, e.g. epoxy, is injected intothe cavity making an anchoring for the wires.

The carcass 2 is fastened to the end-fitting 9 by means of a lock nut15, and to the inner lining 3 by means of a lock ring 16 fitting into anannular groove 17 in the wall of the through opening 14. The lock ring16 is in the embodiment shown secured in the groove 17 by a castingmaterial 18, e.g. epoxy, which is injected through a hole 19.

A ring 20 provides a stop for the lock nut 15. In the embodiment shown asealing ring 21 for tightening the end-fitting 9 and the inner lining 3is fitted into a groove 22 in the ring 20.

As best seen in FIG. 3 the carcass consists of helically wound metallicstrips 23 forming a screwthread 24 with windings 25.

After having removed the layers 3, 4, 5, 7 surrounding the carcass 2 atthe end of the pipe, the lock nut 15 simply is screwed on to the end ofthe carcass whereafter said end is inserted into the through opening 14of the end-fitting 9, with the lock nut 15 placed in a annular holdinggroove 28 formed in the wall of the through opening.

For some applications the lock nut 15 can also be embedded in a castingmaterial (not shown), e.g. epoxy, for fixing the lock nut firmly in theholding groove of the end-fitting.

The lock nut 15 is locked to the carcass 2 by screwing a screw 26radially into the lock nut and into the carcass. When the carcass hasbeen to some extent unwound, this screw can be used for rotating thelock nut such that the windings 25 of the carcass 2 are tightened up.

Between the lock nut and the end-fitting a galvanic potential couldpossibly arise. The surface of the lock nut 15 therefore has a coating27 of a galvanic insulation material, e.g. PTFE, for preventingcorrosion of the two parts which could be caused by such a potential.The insulating material may include solid insulation material forimproving the pressure strength of the material.

In the embodiment shown, the lock nut is coated with the insulatingmaterial, but the lock nut can in another embodiment (not shown) consisttotally of this material .

The insulating material can also simply be in the form of annular discs(not shown) placed on each side of the lock nut.

Having thus provided a general discussion, and specific illustrations byway of examples, it is to be understood that no undue restrictions areto be imposed by reason thereof. Many other embodiments are imaginablewithin the scope of the invention. The specific locking, according tothe invention, between the carcass 2 of the flexible pressure pipe 1 andthe end-fitting 9 can be used in combination with other constructions ofthe joint between the end-fitting 9 and the tensile armour wires 6 andthe inner lining 3, respectively, in addition to those described aboveand shown in the figures.

What is claimed is:
 1. An assembly of an end-fitting, having an axiallyextending through opening, with a flexible pressure pipe which is of anon-bonded structure comprising a number of layers including an innercarcass of an interlocking structure made from metallic strips forming ascrewthread, an end part of which extends, in assembled condition, intothe through opening wherein the assembly comprises an annular holdinggroove which is formed in the wall of the through opening, and a locknut which is screwed on the screwthread-form strips of the end part ofthe carcass and fitted directly into the holding groove after havingremoved at least the immediate to the carcass situated layers in thearea of the lock nut.
 2. An assembly according to claim 1, wherein inthat it comprises at least one screw (26), which is screwed radiallyinto the lock nut (15) and against the carcass (2).
 3. An assemblyaccording to claim 1, wherein in that there is a gap between the locknut (15) and the holding groove (28), and that this gap is filled with acasting material, e.g. a polymer such as epoxy.
 4. An assembly accordingto claim 1, wherein it further comprises a galvanic insulation materialwhich is interposed between the lock nut (15) and the end-fitting (9).5. An assembly according to claim 4, wherein in that the galvanicinsulation material is of a type having a high electrical resistance. 6.An assembly according to claim 4 or claim 5, wherein in that thegalvanic insulation material is PTFE.
 7. An assembly according to claim4 or claim 5, wherein in that the galvanic insulation material is PTFEwhich is filled with solid insulation material.
 8. An assembly accordingto claim 4, wherein in that the galvanic insulation material is in theform of an annular disc, placed on each side of the lock nut (15).
 9. Anassembly according to claim 4, wherein that the lock nut (15) is coatedwith or consists of the galvanic insulation material.
 10. A method forassembling an end-fitting, having an axially extending through opening,with a flexible pressure pipe which is of a non-bonded structurecomprising a number of layers including an inner carcass of aninterlocking structure made from metallic strips forming a screwthread,an end part of which extends, in the assembled condition, into thethrough opening wherein the method comprises, removing the layerssurrounding the carcass at an end of the pipe, screwing a lock nut on tothe screwthread-form strips of the end part of the carcass, and directlyplacing the lock nut in a holding groove formed in the wall of thethrough opening.